The invention relates to the field of intravascular balloon catheters, and more particularly to a catheter balloon having a stepped outer diameter that provides for improved dilatation and stenting.
In percutaneous transluminal coronary angioplasty (PTCA) procedures a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced into the patient's coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. at least about 8 atmospheres) so that the stenosis is compressed against the arterial wall to open up the passageway. Preferably, the inflated diameter of the working length of the balloon is approximately the same as the native diameter of the body lumen being dilated, so as to complete the dilatation but not overexpand the artery wall. However, damage to the vessel wall at and around the stenosis can result from the expansion of the balloon against the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated vessel and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. Further details of stents and stent delivery systems can be found in U.S. Pat. Nos. 5,507,768 (Lau et al.), 5,458,615 (Klemm et al.), and 5,514,154 (Lau et al.), which are incorporated herein by reference in their entireties. Thus, stents are used to open a stenosed vessel, and strengthen the dilated area by remaining inside the vessel. Although stents have been used for some time, the effectiveness of a stent can be diminished if it is not properly implanted within the vessel. One difficulty has been deploying the stent at the desired location in the vessel and completely expanding the stent during the deployment.
Therefore, what has been needed is an improved balloon catheter with a balloon which expands to dilatate a stenosis or to deploy a stent within the patient. The present invention satisfies these and other needs.